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| United States Patent |
5,084,356
|
|
Deak
, et al.
|
January 28, 1992
|
Film coated with glass barrier layer with metal dopant
Abstract
A structure comprising a polymeric film substrate and a glassy coating of
silicon dioxide heavily doped with at least one metal selected from the
group consisting of antimony, aluminum, chromium, cobalt, copper, indium,
iron, lead, manganese, tin, titanium, tungsten, zinc, and zirconium,
provides improved barrier properties.
| Inventors:
|
Deak; Gedeon I. (Wilmington, DE);
Jackson; Scott C. (Kennett Square, PA)
|
| Assignee:
|
E. I. du Pont de Nemours and Company (Wilmington, DE)
|
| Appl. No.:
|
513302 |
| Filed:
|
April 20, 1990 |
| Current U.S. Class: |
428/458; 428/412; 428/417; 428/446; 428/474.4; 428/480 |
| Intern'l Class: |
B32B 015/08 |
| Field of Search: |
428/446,458,480,412,417,474.4
|
References Cited
U.S. Patent Documents
| 3442686 | May., 1969 | Jones.
| |
| 3522080 | Jul., 1970 | Dietzel et al.
| |
| 3808027 | Apr., 1974 | Anderson et al.
| |
| 4312915 | Jan., 1982 | Fan | 428/469.
|
| 4528234 | Jul., 1985 | Kaibo et al.
| |
| 4552791 | Nov., 1985 | Hahn.
| |
| 4702963 | Oct., 1987 | Phillips et al.
| |
| Foreign Patent Documents |
| 61-47244 | Mar., 1986 | JP.
| |
| 60-244540 | Dec., 1986 | JP.
| |
| 62-156943 | Jul., 1987 | JP.
| |
| 62-158677 | Jul., 1987 | JP.
| |
| 2197881 | Jun., 1988 | GB.
| |
Other References
Chahroudi, "Glassy Barriers from Electron Beam Web Coaters", 5/4/89.
Sakamaki, "Vapor Coating with Silicon Dioxide", 5/23/89.
|
Primary Examiner: Cashion, Jr.; Merrell C.
Assistant Examiner: Le; Hoa T.
Attorney, Agent or Firm: Shold; David M.
Claims
We claim:
1. A structure having superior barrier properties, comprising:
(a) a polymeric substrate, and
(b) a glassy coating of silicon dioxide doped with at least one metal
selected from the group consisting of antimony, aluminum, chromium,
cobalt, copper, indium, iron, lead, manganese, tin, titanium, tungsten,
zinc, and zirconium, said coating and metal dopant contained therein being
present in an amount suitable to provide an oxygen transmission value
through the coated structure of at most about 5 mL/day-m.sup.2 -atm.
2. The structure of claim 1 wherein the amount of glassy coating and the
amount of metal dopant contained therein are suitable to provide an oxygen
transmission value through the coated structure of at most about 1.5
mL/day-m.sup.2 -atm.
3. The structure of claim 1 wherein the amount of metal dopant is suitable
to provide an oxygen permeation value for said glassy coating of at most
about 3000.times.10.sup.-6 mL-mm/day-m.sup.2 -atm.
4. The structure of claim 1 wherein the amount of metal dopant is suitable
to provide an oxygen permeation value for said glassy ooating of at most
about 600.times.10.sup.-6 mL-mm/day-m.sup.2 -atm.
5. The structure of claim 1 wherein the amount of metal dopant is suitable
to provide an oxygen permeation value for said glassy coating of at most
about 400.times.10.sup.-6 mL-mm/day-m.sup.2 -atm.
6. The structure of claim 1 wherein the thickness of the glassy coating is
about 20 to about 500 nm.
7. The structure of claim 6 wherein the thickness of the glassy coating is
about 50 to about 350 nm.
8. The structure of claim 1 wherein the glassy coating of silicon dioxide
is doped with a metal selected from the group consisting of copper,
chromium, manganese, tin, and zinc.
9. The structure of claim 8 wherein the metal is copper.
10. The structure of claim 8 wherein the metal is tin.
11. The structure of claim 1 wherein the amount of dopant metal is
sufficiently low that the optical density of said glassy coating retains
at least about 70% optical transmission at 550 nm.
12. The structure of claim 1 wherein the amount of dopant metal calculated
as elemental metal is about 0.5 to about 30 weight percent of the glassy
coating.
13. The structure of claim 9 wherein the amount of copper in the glassy
coating is about 1 to about 15 weight percent.
14. The structure of claim 10 wherein the amount of tin in the glassy
coating is about 3 to about 30 weight percent.
15. The structure of claim 1 wherein the polymeric substrate is a film.
16. A multiple layer structure comprising the structure of claim 15 as at
least one layer.
17. The structure of claim 1 wherein the polymeric substrate has a surface
smoothness such that the average height of roughness is less than about 50
nanometers.
18. The structure of claim 1 wherein the polymeric substrate has a surface
smoothness such that the average height of roughness is less than about 10
nanometers.
19. The structure of claim 15 wherein the substrate film is polyester or
polyamide.
20. The structure of claim 19 wherein the substrate film is oriented
polyethylene terephthalate.
21. The structure of claim 1 further comprising a plastic resin protective
layer.
22. A structure having superior barrier properties, comprising:
(a) a polymeric substrate, and
(b) a glassy coating of silicon dioxide doped with lithium borate in an
amount suitable to provide an oxygen transmission value through the coated
structure of at most about 5 mL/day-m.sup.2 -atm.
Description
BACKGROUND OF THE INVENTION
This invention relates to polymeric films having improved barrier
properties towards oxygen and other materials.
Flexible polymer films have been used extensively in the packaging of food,
electronic and medical products. It is desirable in many applications to
have a good barrier to oxygen and/or water vapor. However, most polymer
based barrier resins such as ethylene vinyl alcohol copolymer ("EVOH") or
polyvinylidene chloride ("PVDC"), although exhibiting good barriers to
oxygen or moisture, do so only under ideal conditions. Although EVOH can
be an excellent oxygen barrier, it looses its barrier property at moderate
to high relative humidity. Thus this material is not widely usable in
applications involving high water vapor content, such as moist foods.
Although PVDC exhibits good moisture and oxygen barrier properties, it is
not suitable for many applications, has an undesirable yellow color, and
is difficult if not impossible to recycle. Other proposed alternatives to
provide oxygen and water vapor barriers include laminations of aluminum
foil and aluminum metallized film. Although these exhibit good barrier
properties, they are completely opaque, cannot be recycled, and cannot be
readily used for food packaging destined for use in a microwave oven.
U.S. Pat. No. 4,702,963 discloses packaging film in which an adhesion layer
is first vacuum deposited on a flexible polymer substrate, followed by
vacuum deposition of a barrier layer, to confer retortability to the
packaging film. The adhesion layer can consist of Cr, which is preferred,
co-deposited mixtures of Cr and SiO having at least 20% by weight Cr,
among others. The barrier layer is preferably silicon monoxide or silicon
dioxide. When silicon dioxide is used, it may be mixed with glass
modifiers such as oxides of Mg, Ba, and Ca, or with fluoride of alkaline
earth metals, e.g. MgF.sub.2. The glass modifiers serve to alter the color
appearance of the overall coating. For example, a chromium/SiO composite
film is disclosed to produce a coating with a yellowish appearance, while
a neutral gray appearance is disclosed to result from the mixture of
SiO.sub.2 with glass modifiers.
Japanese patent application 60-244540 discloses a laminate comprising the
formation on the surface of a plastic film a transparent thin layer of one
or more materials selected from metals, metal oxides, or glass by means of
a dry plating method, providing a laminate with good barrier properties.
Suitable metals include aluminum, silicon, iron, gold, silver, copper,
chromium, nickel, tin, titanium, and magnesium. Suitable oxides may be the
oxides of these metals (such as silicon oxide, which can be mixtures of
silicon monoxide and silicon dioxide), and glass. A mixed evaporation or
multilayer evaporation may be performed.
Japanese patent application 61-47244 discloses a laminate of a plastic film
or sheet on the surface of which has been formed a transparent thin layer
by dry plating one or more of the materials selected from metals, oxides
of the metals, and glass. Suitable metals include aluminum, silicon,
titanium, tin, iron, gold, silver, copper, chromium, nickel, magnesium, or
the like. The oxides are those of these metals, or glass. These metals and
metal oxides may be evaporated in a mixed state to form a layer or
evaporated to form a multilayer. The laminate is said to have excellent
gas-barrier performance.
U.S. Pat. No. 4,528,234 discloses a transparent laminate comprising a
transparent plastic resin film substrate, a thin layer of at least one
metal such as aluminum, tin, iron, zinc, or magnesium formed on the
substrate by vacuum deposition, and a carboxyl group-containing polyolefin
(e.g. ionomer)
layer formed on the metal layer by lamination. Optionally an additional
layer of silicon oxide or titanium oxide may be present. Oxygen and
moisture impermeability are said to be improved.
U.S. Pat. No. 3,442,686 discloses a composite film structure suitable as a
packaging film consisting of a flexible transparent organic base sheet,
e.g. PET film, having a top coating of a polymer such as polyethylene and
an intermediate, gas barrier, glassy coating of an inorganic material such
as a silicon oxide. Other inorganic compositions which are useful include
lead chloride, silver chloride, calcium silicate, and crushed "Alundum"
(Al.sub.2 O.sub.3 with SiO.sub.2 binder).
Japanese patent application 62-158677 discloses a transparent laminate
wrapping material where a thin single or mixed metal oxide layer is an
intermediate layer in a laminate structure. The laminate is said to have
excellent gaseous oxygen and water vapor barrier properties. Silicon oxide
and aluminum oxide-silicon oxide mixtures are effective.
Japanese patent application 62-156943 discloses a vapor-deposited layer
built-in type multilayered gas-barrier film or sheet having two or more
vapor-deposited layers of metals or metal compounds formed at one or more
laminate interfaces of a multilayered synthetic resin film or sheet,
having good gas barrier characteristics. Suitable metals include aluminum,
zinc, copper, platinum, indium, tin, gold, silver, and silicon. A suitable
metal compound is silicon oxide.
Chahroudi, "Glassy Barriers from Electron Beam Web Coaters," paper
presented at Annual Technical Meeting of Society of Vacuum Coaters,
discloses barriers of silicon oxide or SiO.sub.2. Oxides of Mg, Ca, Ba, B,
Al, In, Ge, Sn, Zn, Ti, Zr, Ce, and MgF.sub.2 are disclosed as modifiers
or replacements for silica.
Sakamaki, "Vapor Coating with Silicon Dioxide," discloses barrier
properties of film with a thin layer of ceramic such as SiO.sub.x, in
particular silicon oxide.
U.S. Pat. No. 3,522,080 discloses a process for hardening the surface of a
synthetic material such as a lacquer film, which includes vapor deposition
of layers of silicon oxide (SiO.sub.x derived from SiO.sub.2) onto the
surface. The silicon oxide can contain 1.5 to 5 percent oxide of chromium,
zinc, zirconium, or antimony.
U.K. patent application 2 197 881 discloses a heat resistant vessel made of
a thermoplastic polyester resin by forming an inorganic coating layer
comprising a silicon compound or a metal oxide-containing silicon compound
on a surface of the polyester resin. The inorganic coating layer is
obtainable from colloidal polysiloxane compounds. The coating material may
further contain additives such as an inorganic filler of e.g. titanium
oxide, zirconium silicate, nickel, copper oxide, manganese oxide, alumina,
etc.
In certain of the above references, coatings of silicon monoxide (SiO),
silicon dioxide (SiO.sub.2), or combinations thereof with a variety of
metal oxides have been disclosed. There has been lacking, however,
teaching as to the type and quantity of metal or metal oxide required to
provide coatings of SiO.sub.2 with improved barrier properties. It has now
been observed that combinations of SiO.sub.2 with many metals or metal
oxides in fact do not provide improved barrier performance or
alternatively reduce the optical transparency of films coated therewith to
an objectionable extent. Furthermore, much of the prior art focuses on SiO
as the primary barrier layer. The use of SiO is not practical for many
packaging applications because it is quite expensive and exhibits an
objectionable yellow color. The present invention, in contrast, overcomes
these shortcomings by providing an inexpensive inorganic coating with good
barrier performance and good light and microwave transparency, suitable
for packaging applications.
SUMMARY OF THE INVENTION
The present invention provides a structure having superior barrier
properties, comprising a polymeric substrate and a glassy coating of
silicon dioxide doped with at least one metal selected from the group
consisting of antimony, aluminum, chromium, cobalt, copper, indium, iron,
lead, manganese, tin, titanium, tungsten, zinc, and zirconium, said
coating and metal dopant contained therein being present in an amount
which provides an oxygen transmission value through the coated film
structure of at most about 5 mL/day-m.sup.2 -atm. Preferably the amount of
metal dopant is sufficient to provide an oxygen permeation value for the
glassy coating of at most about 3000.times.10.sup.-6 mL-mm/day-m.sup.2
-atm. The structure may be a film and may comprise one or more layers of a
multiple layer structure.
The invention further provides a process for imparting barrier properties
to a polymeric substrate, comprising the steps of selecting a polymeric
substrate and vacuum depositing onto the substrate a glassy coating
prepared from silicon dioxide and at least one metal selected from the
group consisting of antimony, aluminum, chromium, cobalt, copper, indium,
iron, lead, manganese, tin, titanium, tungsten, zinc, and zirconium,
wherein the amount of said glassy coating and the amount of metal
contained therein is suitable to provide an oxygen transmission value
through said film structure of at most about 5 mL/day-m.sup.2 -atm.
The present invention further provides a similar structure and process in
which the dopant is lithium borate.
DETAILED DESCRIPTION OF THE INVENTION
The barrier films of the present inventions are polymeric substrates such
as films, coated directly or indirectly with specially selected glass
coatings. The polymeric substrates include any having suitable physical
and thermal properties for the particular packaging application at hand.
The minimum requirement is that they have sufficient thermal and physical
properties to withstand the conditions of application of the glass
coating, described in more detail below, and exhibit sufficient adhesion
to the class coating. Examples of suitable substrates include those
prepared from polyamides, including amorphous and semicrystalline
polyamides, polycarbonates, polyethers, polyketones, polyester ethers, and
polyesters, which are preferred.
Examples of polyester resins include polyethylene naphthalate and most
preferably polyethylene terephthalate ("PET"). Examples of semicrystalline
polyamides include polycaprolactam (nylon 6) and condensation polymers of
dicarboxylic acids and diamines, such as polyhexamethylene adipamide
(nylon 6,6) etc. Examples of amorphous polyamides include
hexamethylenediamine isophthalamide, hexamethylenediamine
isophthalamide/terephthalamide terpolymer, having iso/terephthalic moiety
ratios of 100/0 to 60/40, mixtures of 2,2,4- and
2,4,4-trimethylhexamethylenediamine terephthalamide, copolymers of
hexamethylene diamine and 2-methylpentamethylenediame with iso- or
terephthalic acids, or mixtures of these acids. Polyamides based on
hexamethylenediamine iso/terephthalamide containing high levels of
terephthalic acid moiety may also be useful particularly when a second
diamine such as 2-methyldiaminopentane is incorporated to produce a
processible amorphous polymer. Typically a substrate, especially a film,
will have been oriented, optionally followed by heat setting so as to
provide dimensional and thermal stability.
It is preferred that the substrate has a high surface smoothness. In
particular when the substrate is polyethylene terephthalate it is
preferred that the substrate have a smoothness such that the average
height of roughness is less than about 50 nanometers, and most preferably
less than about 10 nanometers, as measured on a WYKO.TM. optical
profilometer, Model TOPO-3D from WYKO Co., Tuscon, Ariz. Most ordinary PET
films have a relatively large degree of surface roughness because of the
presence of various internal anti-block and slip additives which are
necessary to improve handling properties. An oriented PET film without
such additives will have a very smooth surface but cannot generally be
handled, i.e., wound and rewound, without introducing excessive wrinkling.
However, a practical film with preferred smoothness can be prepared by
selectively treating only one surface with a selected antiblock agent,
leaving the other surface untreated and smooth. Application of such an
agent to at least one surface of a film is described in U.S. Pat. No.
3,808,027, the disclosure of which is incorporated herein by reference. A
preferred commercially available substrate is Mylar.RTM. polyester film,
type D, which has a surface roughness of 2-7 nm. It is believed that films
with this superior level of smoothness provide better adhesion of the
glass coating to the film, leading in certain instances to improved
barrier properties and improved stability under retort conditions. It is
preferred that the glassy coating be applied to the smooth side of such
film.
A layer of doped glass is applied to the substrate. This layer can be
applied directly to the substrate, or it can be applied indirectly, i.e.,
atop one or more intermediate layers which are themselves located on the
substrate. One such intermediate layer, for example, can be silicon oxide,
which is described in more detail below. The doped glass coating should be
thick enough to adequately improve the barrier properties of the
substrate, but not so thick as to seriously degrade transparency of the
substrate or to result in loss of durability or flexibility of the glass,
when the substrate is a film. Typically coatings of about 20 to about 500
nm are suitable, depending on the effectiveness of the particular glass
composition. A thickness of about 50 to about 350 nm is preferred,
although for some compositions a thickness of about 200 to 400 nm is
desirable; for particularly effective compositions, a coating of 50 to 100
nm is quite adequate.
The doped glass coating is based on silicon dioxide. The actual
stoichiometry of the glass in this layer may vary from the nominal
oxygen-silicon ratio of 2:1 of SiO.sub.2, for example, due to reactions
which may occur during the vacuum deposition process. The glass coating is
generally applied to the substrate in a batch or continuous process by any
of a variety of conventional vacuum methods. The portion of the substrate
to be coated is positioned either by a continuous process or batch process
in a chamber within which a vacuum is drawn. A source of silicon dioxide
and dopant metal (in either different sources or comixed in a single
source, either as a powder, a metal wire, or vitrified into a silica
glass) is placed in the vacuum chamber and vaporized by heating with an
electron beam or a resistance or induction heated furnace, or by
sputtering or reactive sputtering by an ion beam or a magnetron source, or
the like. The silicon dioxide, along with the dopant metal, condenses to
form the desired coating. The thickness of the coating is determined by
the residence time of the substrate in the chamber, the amount of oxide
target present in the chamber relative to the area of the substrate,
and/or the energy delivered to the source per unit area of the source.
When the resin substrate is in the form of a film, the film may be made
inaccessible to the vacuum deposition on one surface thereof so that only
the opposite surface receives the vacuum deposited layers. When the resin
substrate is in the form of a container, the entire container can be
positioned within the vacuum chamber. The surface of the resin substrate
facing the source receives the vacuum deposited coatings. The substrate
can be repositioned and the coating operations repeated to cover
additional surfaces, such as the opposite side, of the substrate.
Sufficient vacuum is drawn within the vacuum chamber that the mean free
path of the silicon dioxide and dopant molecules is sufficient to reach
and therefore enable deposition of the glassy layer on the resin
substrate. The vacuum used in the experiments described in the Examples
herein generally falls within the range of about 1 to 100 microtorr (760
torr =1 atm). One skilled in the art will know how to select the proper
vacuum for a given vacuum deposition process, including its conditions of
operation.
The dopant can be incorporated into the SiO.sub.2 layer either by
evaporating a single source of a physical or fused mixture of the dopant
and SiO.sub.2, or by co-depositing the dopant and the SiO.sub.2 from two
or more sources simultaneously. In both cases, the dopant can be in a
metallic form or in the form of an oxide, silicide, silicate, halide, or
carbonate, and the like. In the case of depositing from a single source,
the proportion of the dopant present in the deposited SiO.sub.2 layer may
vary from the composition of the source. Such proportion can be determined
for a particular source composition and conditions of vacuum deposition
and can be adjusted to the proportion desired by adjustment of the source
composition. In case of either deposition method, the composition of the
coating can be determined by analysis of atomic absorption using
inductively coupled plasma (ICP), which is a conventional analysis
procedure. This analysis primarily detects the elemental metal in the
SiO.sub.2. Therefore, the weight percents of dopant disclosed herein are
based on the elemental metal of the metal dopant. Thus decomposition
products, e.g. CO.sub.2 from carbonates, which do not become part of the
SiO.sub.2 layer are not included in weight percents of dopant in that
layer. The weight percents of dopant disclosed herein refer to the
composition of the SiO.sub.2 layer unless otherwise indicated. These same
weight percents may, however, be present in the source(s) for vacuum
deposition (co-deposition), and as previously described, the resultant
composition of the SiO.sub.2 layer for the vacuum deposition conditions
used can then be determined, and the source composition can be adjusted in
subsequent runs to obtain the final composition desired. More often, the
source composition will be adjusted to provide the barrier properties
desired for the multilayer structure rather than analyzing the SiO.sub.2
layer for its dopant content.
The silicon dioxide coating of the present invention is "doped," as
described above, with a high level of at least one of a select group of
metals. The term "doping" is used herein to describe a deposition with
silicon dioxide of a relatively high level of metal, typically 0.5 to
about 25 weight percent, as measured in the source, or about 0.5 to about
30 weight percent as measured as metal in the glass coating itself. (It is
understood that the term "doped" or "doping" previously has been used in
the art to refer to lower levels of metal additive, typically well below
1%. This is not what is meant by "doped" in the context of the present
invention.)
The oxidation state of the metal as it resides in the coating matrix of
silicon dioxide is not necessarily clearly understood or well defined.
Thus if an elemental metal is used as the source for the dopant, the
deposited metal atoms or particles may interact with the oxygen atoms of
the matrix to form a partially or completely oxidized material.
Alternatively, if an oxide of the metal is used as the source, it is not
necessarily known nor is it necessarily important whether the metal is
deposited into the glassy matrix as the oxide or as the elemental metal.
It appears that either the elemental metal or an oxide of the metal or
certain other metal compounds, regardless of oxidation state can be
suitably used as the source of the dopant metal for the present invention.
Such possibilities and equivalents thereof are included within the scope
of the present invention when terms such as "metal dopant" or the like are
used. The selection of an appropriate source for metal dopant will be
within the abilities of one skilled in the art and will be determined by
such factors as relative cost and ease of handling. In many cases the
metal oxide or especially the elemental metal will be preferred.
Suitable metal dopants for the present invention include antimony,
aluminum, chromium, cobalt, copper, indium, iron, lead, manganese, tin,
titanium, tungsten, zinc, and zirconium. Preferred metals include
chromium, manganese, zinc, and most preferably copper and tin. When one or
more of these metals are present, the barrier property of the glass
coating and of the structure as a whole is greatly improved. Surprisingly
it has been found that many other metals do not show this sort of
improvement. Among the metals that are not particularly effective at
comparable levels are calcium, vanadium, lithium, nickel, molybdenum,
gold, germanium, and selenium. Sulfur is similarly not effective. It is
surprising that these elements appear in the same regions of the periodic
table with the metals that are effective. The chemical phenomenon that
distinguishes between these groups of metals is not understood. It is
noted that the metals which form a part of the present invention are
generally located to the right of Column II of the Periodic Table, that
is, to the right of the alkali metals and the alkaline earth metals.
When a metal dopant from the metals of the present invention is used in the
layer of silicon dioxide, the improvement in barrier properties can be
dramatic. One customary measurement of barrier properties of a film is its
oxygen transmission rate ("OTR", ASTM D-3985-81(1988)) expressed as mL
oxygen passage/m.sup.2 -day-atmosphere. A film of ordinary untreated PET,
23 micrometers thick, typically has an OTR of 75-90; that of a 12
micrometer film is typically 150-180. Addition of a 300 nm coating of
SiO.sub.2 reduces the OTR somewhat, to about 10-80. Addition of one or
more of the metals of the present invention can routinely reduce the OTR
to less than 5. In copper, the most preferred case, addition of even 1
percent to the SiO.sub.2 (measured in the source) can reduce the OTR to as
low as 0.5, while use of 5-10 percent copper can result in values as low
as 0.3. Use of tin, which is also preferred, provides values nearly as
low.
The effectiveness of the barrier properties depends not only on the type of
metal involved but also, of course, on the thickness of the glass layer.
The effect of total glass thickness can be factored out by focusing on the
oxygen permeation value ("OPV," mL-mm,M.sup.2 -day-atm), which provides a
measure of the inherent barrier properties of the glass. A coating of
SiO.sub.2 alone exhibits an OPV on the order of 0.1 or higher. The
coatings of the present invention exhibit OPV of typically
3.times.10.sup.-3 or lower, and in the best cases as low as
1.times.10.sup.-4 or better.
The OTR or OPV of a particular film or composition is not a simple linear
function of dopant concentration. For each metal dopant there appears to
be a certain minimum concentration required to achieve a significant
improvement, a concentration range, varying somewhat with the metal but
generally within about 0.5 to about 30 weight percent (calculated as
elemental metal in total glass layer), where the invention is effective,
and a region of higher metal concentration within which the effectiveness
diminishes or the optical transparency of the film is adversely affected.
It has further been found that in one embodiment of the present invention,
the appearance and resistance of the coated structure to retort conditions
is improved when a thin underlayer of SiO is applied to the substrate.
Further details of this embodiment are set forth in copending U.S.
application Ser. No. 07/513,354 now U.S. Pat. No. 5,085,904 the disclosure
of which is incorporated herein by reference.
In addition to the above described layers, an additional protective layer
can be added. Such a layer can be selected from any plastic resin that
adheres to the SiO.sub.2 layer or that adheres via an intervening adhesive
layer. Examples of protective layers include a layer of polyester (adhered
to the SiO.sub.2 layer via an adhesive), polyamides, acrylonitrile
copolymers, polyvinylidene chloride, polyethylene, polypropylene, ethylene
vinyl acetate copolymer, ethylene/acrylic or methacrylic acid copolymer
and ionomer. The protective layer can be applied to the SiO.sub.2 layer by
conventional processes such as adhesive or thermal laminating or extrusion
coating simultaneous with extrusion of the intervening adhesive, if any.
The protective layer can also be provided by solvent or dispersion coating
onto the SiO.sub.2 layer, using multiple coatings if thickness greater
than achievable by single coating is desired. The thickness of the
protective layer will generally be about 0.5 to 100 micrometers,
preferably 10 to 25 micrometers (0.020 to 0.025 mm).
Films and structures of the present invention are useful as a wide variety
of packaging, from rigid to semi-rigid containers to packaging film where
barrier properties towards oxygen and other materials are desired. The
particular use will dictate the choice and shape of the resin substrate.
For packaging films, the resin substrate will be in the form of a film
having, for example, a thickness of 10 to 150 micrometers, often 12 to 50
or preferably 15 to 25 micrometers.
EXAMPLES 1-136
Silicon dioxide was mixed with a dopant material and loaded into the hearth
(crucible) of an electron beam evaporator of the single crucible bent beam
source type as sold by a variety of manufacturers including Denton Vacuum
of Cherry Hill, NJ. A thin film was formed from this mixture onto the
smoother surface of a 23 micrometer (92 gauge) PET film (Mylar.RTM. type
D) by electron beam evaporation from the mixture. The accelerator voltage
was continuously adjusted to sweep the beam across the material in the
source crucible to give uniform erosion of the crucible's contents. The
filament current (and hence the beam current) was adjusted to provide a
high deposition rate, resulting in a relatively high background pressure
of about 1.3.times.10.sup.-2 Pa (about 1.times.10.sup.-4 torr). This
pressure was not so high as to cause premature arc-over of the electron
beam gun. The thickness of the deposit was monitored by a calibrated
oscillating quartz crystal monitor such as manufactured by Veeco
Instruments Inc., Plainview, N.Y. The film (unless another grade is
reported) had an average (RA) surface roughness of 2-7 nanometers. The
coated film's oxygen transmission rate was measured using an "Ox-Tran
1000.TM." oxygen permeation device manufactured by Modern Control Inc. of
Minneapolis, Minn. All data in Table I were obtained at 30.degree. C. at
80% relative humidity, using 100% oxygen at 1 atmosphere pressure (about
101 kPa). The results are reported in the Tables as oxygen transmission
rate (mL/m.sup.2 -day-atm). In addition the results are reported as oxygen
permeation value (mL-mm/m.sup.2 -day-atm) by subtracting the (minimal)
barrier properties of the uncoated film and dividing the result by the
thickness of the glass coating.
The results for the first Examples, Table I, Examples 1-11, illustrate the
poor barrier properties of PET film treated with a layer of undoped
silicon dioxide.
TABLE I
______________________________________
Ex..sup.a
Dopant Thickness, nm OTR OPV .times. 10.sup.6
______________________________________
C1 none 325 23.6 12054
C2 " 300 84.3 >100000
C3 " 301 76.4 >100000
C4 " 303 77.1 >100000
C5 " 314 7.1 2517
C6 " 315 62.1 >100000
C7 " 323 51.6 83026
C8 " 355 10.1 4238
.sup. C9.sup.b
" -- 161.5 --
.sup. C10.sup.b
" -- 72.4 --
.sup. C11.sup.b
" -- 28.1 --
______________________________________
.sup.a Examples designated "C" are included for comparative purposes.
.sup.b PET film having a surface roughness of 26-33 nm and a thickness of
12 micrometers.
-- indicates value not measured.
The results in the next series of Examples, Table II, Examples 12-57,
illustrate many of the metal dopants which are not a part of the present
invention. Most of these dopants do not provide significant improvements
in barrier properties in the concentration ranges examined, although a few
do show improvement (e.g. MgF.sub.2, MgO, BaO, disclosed in U.S. Pat. No.
4,702,963 along with CaO which does not show adequate activity). For
reasons which are not fully understood, low levels of lithium borate,
Li.sub.2 B.sub.4 O.sub.7, seem to be effective and are thus considered to
be included within the scope of the present invention.
TABLE II
______________________________________
Ex..sup.a
Dopant, % Thickness, nm
OTR OPV .times. 10.sup.6
______________________________________
C12 Ag 10 301 8.5 2944
C13 AgO 10 300 5.9 1944
C14 BaO 10 307 2.6 828
C15 BaO 30 315 7.7 2743
C16 B.sub.2 O.sub.3
3 326 80.3 >100000
C17 B.sub.2 O.sub.3
10 213 77.2 >100000
C18 B.sub.2 O.sub.3
10 327 83.4 >100000
C19 Ca(BO.sub.2).sub.2
10 290 74.7 >100000
C20 Ca(BO.sub.2).sub.2
10 303 35.5 23832
C21 Ca(BO.sub.2).sub.2
25 239 82.5 >100000
C22 Ca(BO.sub.2).sub.2
50 230 73.2 >100000
C23 CaO 10 301 6.0 1985
C24 CaO 30 265 12.3 4042
C25 K.sub.2 O 10 308 27.0 14319
C26 Li 3 -- 80.6 --
27 Li.sub.2 B.sub.4 O.sub.7
1 307 2.5 797
28 Li.sub.2 B.sub.4 O.sub.7
2 301 2.4 756
C29 Li.sub.2 B.sub.4 O.sub.7
7 301 41.5 34897
C30 LiF 1 301 30.1 17002
C31 LiF 4 300 50.4 68597
C32 MgCl.sub.2
2 301 51.7 78306
C33 MgCl.sub.2
10 246 19.0 6639
C34 MgCl.sub.2
10 246 23.3 8955
C35 MgF.sub.2 1 303 20.6 9185
C36 MgF.sub.2 2 299 1.1 320
C37 MgF.sub.2 5 105 4.0 449
C38 MgF.sub.2 5 201 2.2 455
C39 MgF.sub.2 5 303 1.1 334
C40 MgF.sub.2 10 297 1.1 328
C41 MgF.sub.2 10 308 1.1 340
C42 MgF.sub.2 15 306 2.2 713
C43 MgF.sub.2 30 -- 10.2 --
C44 MgO 5 304 1.9 602
C45 MgO 10 302 5.4 1766
C46 MgO 35 215 1.6 341
C47 MgO 35 306 1.6 486
C48 Na.sub.2 B.sub.4 O.sub.7
4 321 29.9 17889
C49 Na.sub.2 B.sub.4 O.sub.7
10 -- 57.2 --
C50 Na.sub.2 B.sub.4 O.sub.7
10 265 66.0 >100000
C51 Na.sub.2 SO.sub.4
5 302 60.2 >100000
C52 Na.sub.2 SO.sub.4
20 304 70.3 >100000
C53 Na + Al.sup.a 301 73.1 >100000
C54 Mo 10 302 72.7 >100000
C55 Ni 10 299 55.8 >100000
C56 Si 10 304 3.3 1073
C57 Si 20 307 1.5 463
______________________________________
.sup.a A fused glass; exact composition unknown.
The next series of Examples, Table III, Examples 58-67, show certain metal
compound dopants (AlF.sub.3, CuCO.sub.3, CuF.sub.2, Cu.sub.5 Si, and
WO.sub.2) which are effective only at comparatively higher concentrations
in the source, e.g., about 20%. It is believed that these materials
evaporate at a slower rate than does SiO.sub.2, resulting in lower actual
concentrations in the films. Yet it is believed that when a sufficient
amount of metal is deposited in the glass coating, the results
nevertheless show significant improvement in barrier properties.
TABLE III
______________________________________
Ex. Dopant, % Thickness, nm
OTR OPV .times. 10.sup.6
______________________________________
C58 AlF.sub.3
2 302 19.5 8445
59 AlF.sub.3
10 313 2.9 961
C60 CuCO.sub.3 --
5 302 15.3 6038
Cu(OH).sub.2
61 CuCO.sub.3
20 300 1.6 491
C62 CuF.sub.2
5 273 9.8 3152
C63 Cu.sub.5 Si
5 308 78.9 >100000
64 Cu.sub.5 Si
20 302 1.9 588
65 Cu.sub.5 Si
20 302 0.9 275
C66 WO.sub.2 5 286 79.9 >100000
67 WO.sub.3 20 123 4.1 537
______________________________________
The last series of Examples, in Table IV, Examples 68-136, illustrate the
results using metal dopants of the present invention. Concentrations of
metal within the effective concentration ranges provide marked
improvements in barrier properties. (In some of the examples using copper,
the metal was added to the source material in the form of a wire; in other
examples, as a powder. No consistent differences in the results were
observed.)
TABLE IV
__________________________________________________________________________
Ex. Dopant,
% Thickness, nm
OTR OPV .times. 10.sup.6
__________________________________________________________________________
68 Al 2 303 1.9 595
69 Al 10 303 1.3 403
70 Al 10 311 1.6 494
71 Al 15 312 4.5 1496
C72.sup.a
Al 30 321 14.3
5875
73 Co 10 214 0.9 196
74 Cr 10 303 1.3 408
75 Cr 20 302 1.9 603
76 Cr 30 300 0.7 207
77 Cr 30 302 1.3 387
C78 Cu 1 300 8.1 2793
C79.sup.a
Cu 1 300 124.0
>100000
80 Cu 1 301 0.5 160
81 Cu 2 26 3.7 102
82 Cu 2 52 4.9 276
83 Cu 2 301 0.7 198
84 Cu 3 303 4.1 1334
85.sup.b
Cu 5 -- 0.7 --
C86 Cu 5 28 11.4
388
87 Cu 5 51 2.1 109
88 Cu 5 100 0.9 90
89 Cu 5 301 0.5 160
90 Cu 5 301 1.0 308
91 Cu 5 303 0.3 80
92.sup.c
Cu 5 305 2.6 829
93.sup.d
Cu 5 300 2.5 770
94.sup.e
Cu 5 295 2.2 658
C95.sup.f
Cu 5 300 7.6 2428
96.sup.g
Cu 5 298 5.1 1712
97.sup.h
Cu 5 300 0.9 271
98.sup.h
Cu 5 302 1.8 567
99.sup.i
Cu 5 301 1.5 527
100 Cu 5 301 0.9 289
C101 Cu 5 303 60.3
>100000
C102 Cu 10 26 7.6 225
103 Cu 10 28 2.9 84
104 Cu 10 51 2.9 155
105 Cu 10 102 3.3 360
106 Cu 10 117 2.1 257
107 Cu 10 301 0.3 94
108 Cu 10 301 0.5 155
109 Cu 15 100 1.3 136
110 Cu 20 301 2.3 726
111 Cu 30 300 0.6 188
C112 Cu,B.sup.k
5 302 74.1
>100000
113 Cu(NO.sub.3).sub.2
5 253 3.5 933
114 Fe 5 302 1.4 421
115 Fe 10 304 3.6 1174
116 In 5 302 1.6 509
117 In 20 309 1.5 476
118 Mn 10 302 0.6 189
119 Pb 10 330 1.5 497
120 Pb 20 309 1.7 526
121 Sb 5 190 5.8 1093
122 Sn 5 302 1.2 358
123 Sn 5 304 1.1 335
124.sup.j
Sn 5 130 1.6 256(est.)
125 Sn 10 150 3.3 524
126 Sn 20 303 1.0 296
127 Sn 30 54 6.2 373
C128.sup.a
Sn 30 54 146.8
>100000
C129.sup.a
316 stainless
10 305 5.3 1767
steel.sup.1
130 TiO.sub.2
10 300 3.8 1200
131 Zn 10 65 6.2 448
132 Zn 10 257 1.4 375
133 Zn 10 296 5.9 1913
134 Zn 20 304 2.2 688
135 ZnO 10 308 1.8 555
Zn 5
136 301 3.9 1262
Cu 2
__________________________________________________________________________
.sup.a Borderline example; results subject to scatter.
.sup.b PET film "Melinex Type 442," surface roughness 10-18 nm. Coating
thickness not measured.
.sup.c PET film having a surface roughness of 10-18 nm and a thickness of
14 micrometers.
.sup.d PET film having a surface roughness of 26-33 nm and a thickness of
12 micrometers.
.sup.e PET film having a surface roughness of greater than 26 nm and a
thickness of 23 micrometers.
.sup.f Polyester film having a surface roughness of 41-49 nm and a
thickness of 12 micrometers.
.sup.g Laminate of the coated film to a layer of uncoated 12 micrometer
PET, using copolyester adhesive sheet.
.sup.h Laminate of the coated film to a layer of PET having a coating of
heat sealable polyester copolymer, using copolyester adhesive sheet.
.sup.i Laminate of the coated film to a layer of PET coated with PVDC,
using copolyester adhesive sheet.
.sup.j Substrate film poly(ethylene2,6-napthalene dicarboxylate with 30 n
undercoating of SiO.
.sup.k Fused silica glass containing Cu and B.
.sup.l 18% Cr, 11% Ni, 2.5% Mo, <0.1% C, remainder Fe.
EXAMPLES 137-175
In the previous Tables the amount of dopant is listed as the amount present
in the source in the hearth of the evaporator. The actual amount present
in the glass coating was independently measured for some samples by atomic
absorption. About 2-2.5 g of the sample is weighed accurately and charred
with concentrated sulfuric acid, then dissolved by addition of
concentrated nitric acid (aqua regia) and concentrated hydrofluoric acid
and heating. The solution is diluted to 100 mL and analyzed by an Applied
Research Laboratories 34000 simultaneous inductively coupled plasma
analyzer or a Perkin Elmer 6500 (sequential) inductively coupled plasma
analyzer. The amounts of the reported elements are calculated assuming
that the dopant is the elemental metal and the matrix is SiO.sub.2 (m.w.
60). The results are shown in Table V.
TABLE V
______________________________________
Thickness
Ex. Dopant nm Source %
Coating %
______________________________________
C137 Ag 303 10.0 0.1
C138 B.sub.2 O.sub.3
300 10.0 0.7
C139 MgF.sub.2
302 5.0 0.6
C140 MgF.sub.2
301 10.0 1.0
C141 Mo 301 10.0 13.4
C142 Na.sub.2 B.sub.7 O.sub.4
302 10.0 {2.1 Na}
{1.3 B}
C143 Ni 300 10.0 16.3
144 Al 302 5.0 3.8
145 Al 312 10.0 4.0
146 Al 303 10.0 <1.8
147 Fe 298 5.0 7.4
148 Fe 304 10.0 13.5
149 Cr 301 2.0 3.2
150 Cr 301 5.0 8.8
151 Cr 298 5.0 7.7
152 Cr 304 10.0 14.6
153 Cr 301 10.0 14.1
154 Cu 147 5.0 10.5
155 Cu 299 5.0 0.0
156 Cu 300 5.0 1.5
157 Cu 307 5.0 8.7
158 Cu 310 5.0 7.4
159 Cu 152 10.0 15.8
160 Cu 299 10.0 8.7
161 Cu 303 10.0 6.2
162 Cu 305 10.0 21.2
163 Cu 276 10.0 17.1
164 Cu 301 20.0 30.2
165 Cu 153 20.0 29.8
166 Mn 302 10.0 12.9
167 Sn 301 2.0 8.8
168 Sn 152 5.0 12.2
169 Sn 304 5.0 24.3
170 Sn 302 5.0 17.5
171 Sn 301 5.0 12.0
172 Sn 271 5.0 8.8
173 Sn 153 10.0 14.6
174 Sn 306 10.0 24.7
175 Sn 285 10.0 26.4
______________________________________
The considerable scatter in the analysis of the coating composition is
believed to arise from several sources including inaccuracies in the
atomic absorption technique and the use of a laboratory evaporation method
which uses a powder mixture of the components which may be less
reproducible than desired. However correlations can be obtained which
indicate actual coating compositions with a calculable uncertainty. The
results relating to the metals included in the present invention all
indicate a higher concentration of the dopant metal in the coatings than
in the source, with the possible exception of aluminum and silver. These
trends are believed to be related to the relative vapor pressures of the
metals compared with silicon dioxide. In particular the amount of copper
or chromium in the glassy coating is about 1.4-1.5 times the amount in the
source; the amount of tin in the coating is about 2.4-2.5 times the amount
in the source. Metal compound dopants, for example some metal oxides,
which may have lower vapor pressures than the elemental metals, may
exhibit different correlations from those seen for the elemental metals.
This phenomenon would explain the behavior of the examples in Table III,
which require higher concentrations in the source to be effective.
However, differences in vapor pressure cannot explain the ineffectiveness
of such metals as nickel or molybdenum, which do appear in the coatings in
amounts comparable to those for e.g. copper.
EXAMPLES 176-209
The Examples in Table VI show the effect of increasing dopant levels on
visible light transmission of films prepared according to the procedure of
Examples 1-136 using a batch "bell-jar" process. The visible light
absorbance (from which transmission is calculated) was measured using a
Hewlett-Packard 8452A diode-array UV-vis spectrophotometer, having a
bandwidth of 2 nm, wavelength reproducibility of .+-.0.05 nm, and
stability of <0.002 absorbance units. The device measures the entire UV
and visible absorbance spectrum simultaneously without scanning. The zero
absorbance level was defined using air as the blank. For each film the
absorbance spectrum from 360 to 740 nm was measured and stored on disk.
The absorbances at 400 and 550 nm are reported. It is observed that
percent transmission decreases with increasing dopant level; preferred
films are those which retain at least about 70 percent transmission at 550
nm. Iron, chromium, and tin appear to be preferred in minimizing loss of
optical transmission. Iron appears particularly suitable in this regard
and actually appears to enhance the optical transmission.
TABLE VI
______________________________________
% Transmission
Ex. Dopant, % Thickness (nm)
400 nm 550 nm
______________________________________
C176 (no coating) 85.01 88.71
C177.sup.a
(no coating) 69.25 77.34
C178 none -- 323 81.85 83.18
C179 none 303 75.68 83.56
C180 MgF.sub.2 5 201 88.10 88.10
181 MgF.sub.2 5 306 88.98 90.19
182 MgF.sub.2 10 301 86.90 92.17
C183.sup.b
SF.sub.6 5 306 86.60 87.70
184 Al 5 304 76.21 80.91
185 Al 15 312 38.90 75.86
186 Al 30 321 1.45 28.18
187 Cr 5 304 84.96 88.73
188 Cr 10 152 82.45 82.42
189 Cr 10 303 85.62 90.07
190 Cr 20 76 81.16 83.67
191 Cr 20 153 70.89 78.76
192 Cr 20 302 12.30 31.62
193 Cu 5 300 59.57 71.94
194 Cu 5 301 73.79 81.66
195 Cu 10 117 64.12 72.44
196 Cu 10 311 51.71 71.94
197 Cu 20 78 84.96 88.73
198 Cu 20 155 50.05 61.44
199 Cu 20 301 25.59 39.81
200 Cu 20 302 53.48 65.80
201 Fe 5 302 87.90 89.41
202 Fe 10 304 82.99 89.54
203 Mn 10 302 78.16 83.95
204 Pb 10 330 26.61 41.88
205 Sn 5 302 85.11 88.72
206 Sn 10 150 82.70 85.51
207 Sn 10 311 84.45 85.29
208 Sn 20 76 86.50 90.16
209 Sn 20 303 25.94 36.31
______________________________________
.sup.a Commodity PET film with internal slip additive, 24 micrometers
thick.
.sup.b Coating prepared from lead glass about 70% Pb.
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